<?php

$elves = explode("\n", file_get_contents('./input.txt'));

echo count(
    array_filter(
        $elves,
        static function($elf) {
            [$section1, $section2] = array_map(static fn($section) => explode('-', $section), explode(',', $elf));
            return
                ($section2[0] >= $section1[0] && $section2[1] <= $section1[1])
                ||
                ($section1[0] >= $section2[0] && $section1[1] <= $section2[1])
                ;
        }
    )
);